ESTIMATION OF NITRIC AND NITROUS ACIDS 357
is very much, quicker than with Derarda's alloy, taking only
five minutes as compared with thirty in the latter estimation.
Ifc is therefore advantageous for routine analyses where rapidity
is an important factor.
A criticism of the method is given by Seydel and Wickers,1
who state that the method is liable to give high results in
the presence of much organic matter. It is useful, however,
for the estimation, of most commercial nitrates and nitric
acids. The normal method of carrying out the estimation is
as follows:—
About 0-5 gram of the nitrate., dissolved in 10-15 c.c. of
water, is placed in a flask of 500-700 c.c. capacity provided
with aKjeldahl soda trap; 10 c.c. of sulphuric acid, containing
about 50 per cent. H2S04 are then added, and 5 grams com-
mercial reduced iron. The flask is gently heated and finally
Tbrouglit to boiling after about five minutes. The contents
of the flask are then, diluted with 50 c.c. of water, made alkaline
"by the addition of 25 c.c. of 30 per cent. NaOH, and the
ammonia distilled off in the ordinary way.
A detailed description of the method with the modification
"by Bochmann will "be found in Lunge and Keane's Tech.
Methods of CTiem. Analysis, Vol. I, p. 311.
Pozzi-Escott Method.
Pozzi Escott 2 recommends the use of aluminium amalgam
in alkaline solution ior the reduction of nitrates and nitric
acid. The nitrate (0-5 gram) is put in a* distilling flask fitted
with a soda trap, 5-6 grams of aluminium cuttings are added,
and 2 c.c. of a saturated solution of mercuric chloride, and
150-200 c.c. of water. The procedure is then similar to the
Devarda process. la order to decompose traces of ammoniated
mercury compounds, a few c.c. of sodium hypophospMte
solutioa are added towards the end.
Frafoot3 finds that simple reduction of nitrates "by alumin-
ium in alkaline solution yields accurate results, and considers
that the amalgam recommended by Pozzi Escott introduces
an unnecessary complication. FraTbot gives the following
particulars for reduction hy aluminium:—
1 Zeitxh. angew. Chern., 1911, 43, 2046.
2 Ann. Ghim. anal., 1909, 14, 445 ; Compt. rend., 1909, 149, 1380
3 Ann, Ohin, anal, 1910, 15, 219.